This invention relates to an apparatus for monitoring the rate of liquid flow in a liquid conveying apparatus. More particularly, this invention relates to an apparatus for measuring the drop volume of a liquid in an I.V. administration set by utilizing a section of relatively narrow tubing into which the drops are directed and the length of the drop is optically and electronically measured by passage past two spaced apart liquid sensors.
A drop volume measuring apparatus is described in U.S. Pat. No. 2,880,764 wherein two light sources are employed to measure the volume of a falling drop. Two beams of light are utilized in U.S. Pat. No. 3,563,090 for liquid drop monitoring and a single capacitive detector with two electrodes is described in U.S. Pat. No. 3,500,366. In U.S. Pat. No. 3,826,137, an apparatus is described for measuring liquid flow which employs a capillary tube into which a liquid flows from a nozzle forming a stream of drops. The drops then freely fall from a nozzle where they are counted prior to falling into the capillary tube. By placing the nozzle in such a manner that the drops contact the surface of the liquid in the tubing, a drop forming gap is provided which is stated to afford accurate determination of the drop count. As there is no detection means associated with the particular drop forming mechanism, this must be done manually. In U.S. Pat. No. 3,898,637, a detection means for gas entering a human blood system from extracorporeal, tubing is described. In this particular unit, electronic detection means is afforded and placed in conjunction with a controlled restriction for the purpose of air bubble detection.
The prior art does not provide an accurate method of measuring the volume of liquid in an I.V. administration set wherein the velocity of liquid in a column is measured by means of two spaced apart liquid sensors. The prior art is either concerned with methods of forming or measuring drops of liquid, or with an electronic detection means used to restrict bubbles in a bubble detection system.
It is an advantage of the present invention to provide a means of monitoring I.V. medication by liquid column measurement which actually measures the length and velocity of flow of the liquid column. Other advantages are a volumetric drop measuring flow meter which is easily adapted to I.V. administration apparatus; can be utilized in conjunction with the usual I.V. administration drip chamber; can be manufactured in such a manner that the disposable portion is relatively inexpensive; and lends itself to be easily integrated with various electronic functions.